A circuit board structure and protection device with integrated thermal fuse

Abstract

This utility model relates to the field of thermal fuse technology, and particularly to a circuit structure and protection device for an integrated thermal fuse. The circuit structure includes a circuit board, a temperature-sensing alloy, and a housing. The circuit board has at least two solder pads; the temperature-sensing alloy is soldered onto the two solder pads to form a conductive circuit; the housing is connected to the circuit board, and the temperature-sensing alloy is sealed within the cavity formed by the housing and the circuit board. Through this design, an integrated thermal fuse is achieved within the limited space of the circuit board, while avoiding the risk of high-temperature damage during installation, thereby effectively improving product performance.

Description

Technical Field

[0001] This utility model relates to the field of temperature fuse technology, and in particular to a circuit board structure and protection device for integrating a temperature fuse. Background Technology

[0002] As consumer electronics, wearable devices, and other products become increasingly miniaturized and highly integrated, circuit board space is becoming increasingly compact, placing stringent requirements on the size and installation reliability of protective devices such as thermal fuses. Traditional thermal fuses typically employ an independent package structure, including leads, a temperature sensing element, flux, a housing, and sealing adhesive. The housing must completely enclose the internal components, and the leads must have reserved mounting dimensions, resulting in a relatively large overall product size that is difficult to adapt to the space requirements of miniaturized circuit boards.

[0003] Meanwhile, the traditional connection method between the thermal fuse pins and the circuit board increases the heat conduction path, reduces the temperature response speed, and makes it difficult to meet the requirements of high-precision over-temperature protection. Utility Model Content

[0004] This utility model provides a circuit board structure and protection device with an integrated thermal fuse, which can solve at least one problem in the background art to achieve the integrated design of the thermal fuse within a limited circuit board space.

[0005] In a first aspect, embodiments of the present invention provide a circuit board structure with an integrated thermal fuse, comprising: A circuit board having at least two solder pad electrodes. A temperature-sensitive alloy is welded onto two electrode pads to form a conductive circuit. The housing is connected to the circuit board, and the temperature-sensitive alloy is sealed within the cavity formed by the housing and the circuit board.

[0006] In one embodiment, the circuit board has recesses or protrusions for positioning the housing, and / or the housing has protrusions and recesses for positioning in conjunction with the circuit board.

[0007] In one embodiment, the outer shell is a ceramic shell, a plastic shell, or a pre-formed film shell; when the outer shell is a pre-formed film shell, the material of the outer shell is PET, PEN, PA, PC, PVDF, PTFE, PI, PE, PP, PVC, or PS.

[0008] In one embodiment, the circuit board is a rigid PCB board or a flexible FPC board; the circuit board is a single-layer board or a multi-layer board.

[0009] In one embodiment, the outer shell is a liquid resin coating structure, wherein the liquid resin includes UV-curable resin or thermosetting resin, and the molding process of the liquid resin includes injection, spraying, brushing, dipping, or roller coating.

[0010] In one embodiment, before the temperature-sensitive alloy is welded to the pad electrode, the thickness of the temperature-sensitive alloy at the welding position to the pad electrode is greater than the thickness of the temperature-sensitive alloy at the non-welding position.

[0011] In one embodiment, after the temperature-sensitive alloy is soldered to the pad electrode, at least a portion of the surface of the temperature-sensitive alloy is in contact with the circuit board on the side closest to the circuit board.

[0012] In one embodiment, the pad electrode is embedded in the circuit board, and the surface of the pad electrode near the temperature-sensitive alloy is flush with the surface of the circuit board near the temperature-sensitive alloy. After being compressed, the lower surface of the temperature-sensitive alloy adheres to the circuit board.

[0013] In one embodiment, the pad electrode is embedded in the circuit board, and a pre-soldering molten layer is provided at the welding position between the temperature-sensitive alloy and the pad electrode, the pre-soldering molten layer increasing the thickness of the temperature-sensitive alloy; the pad electrode is provided with a limiting groove for placing the pre-soldering molten layer, and the lower surface of the temperature-sensitive alloy is attached to the circuit board.

[0014] Secondly, this utility model also provides a protection device, including a circuit board structure employing an integrated thermal fuse as described in any of the above embodiments; the circuit board is provided with a protected element, and at least one end of the protected element is the pad electrode.

[0015] The circuit board structure for the integrated thermal fuse provided by this utility model has at least the following advantages compared to the prior art: 1. Achieve high integration and miniaturization: By directly connecting the temperature-sensing alloy to the pad electrodes of the circuit board, the independent pins and package structure of the traditional temperature fuse are eliminated, significantly reducing the overall size of the device. It can directly adapt to the space requirements of high-density, miniaturized circuit boards and improve the flexibility of circuit layout.

[0016] 2. Improved temperature response speed and protection accuracy: By utilizing the direct contact between the temperature-sensing alloy and the circuit board pads, the heat conduction path is shortened, enabling the temperature-sensing element to detect the actual temperature changes of the circuit board more quickly; at the same time, the flux directly covers the surface of the temperature-sensing alloy, which can quickly promote alloy melting when overheating, further improving the response speed and action accuracy of overheat protection.

[0017] 3. Enhanced packaging reliability and environmental adaptability: The shell is directly connected to the circuit board, forming a closed cavity that seals the temperature-sensing alloy. This effectively prevents interference from the external environment (such as moisture and dust) and avoids the risk of poor contact caused by pin soldering in traditional packaging, thus improving the long-term operational reliability of the device.

[0018] 4. Simplified installation process and reduced costs: The structure design of directly connecting the temperature-sensitive alloy to the circuit board pads simplifies the production process and reduces material and process costs, while avoiding the risk of performance damage to temperature-sensitive devices caused by the high-temperature soldering of traditional pins.

[0019] Other features and beneficial effects of this invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing this invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram of a circuit board structure for an integrated thermal fuse provided in an embodiment of this utility model; Figure 2 This is a schematic diagram of temperature-sensitive alloy welding on a circuit board structure. Figure 3 This is a partial cross-sectional view of the circuit board structure; Figure 4 for Figure 3 A partial sectional view at point A in the middle; Figure 5 , Figure 6 To and Figure 4 Partial sectional views of different variations; Figure 7 This is a schematic diagram of the structure of the temperature-sensitive alloy before welding; Figures 8-11 Partial cross-sectional views of different variations of the combination of the housing and the circuit board.

[0022] Figure label: 1. Circuit board; 11. Pad electrode; 11a. Limiting groove; 12. Recess; 13. Boss; 21. Housing; 21a. Protrusion; 21b. Recess; 22. Flux for breaking; 23. Temperature-sensitive alloy; 24. Pre-soldering fusion layer; 25. Adhesive resin layer; 3. Protected component. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. The technical features designed in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0024] In the description of this utility model, it should be noted that all terms used in this utility model (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this utility model pertains, and should not be construed as limiting this utility model; it should be further understood that the terms used in this utility model should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this utility model.

[0025] Example 1 Please see Figure 1 , Figure 2 This utility model provides a circuit board structure with an integrated temperature fuse, which includes at least: a circuit board 10, a temperature-sensing alloy 23, and a housing 21.

[0026] The circuit board 10 can be made of a rigid substrate or a flexible substrate, with the appropriate substrate and thickness selected based on the specific application requirements. In this embodiment, the circuit board 10 is preferably a rigid PCB (Printed Circuit Board) or a flexible FPC (Flexible Printed Circuit). The circuit board 10 can be a single-layer or multi-layer board; the specific circuit board design can be reasonably adjusted according to actual needs, and this embodiment does not impose any limitations. The circuit board 10 integrates the protected component 3, and the temperature-sensing alloy 23 and the outer shell 21 are integrated on the same copper foil line (pad electrode) connected to the protected component 3 to improve the response speed of the thermal fuse.

[0027] The circuit board 10 has at least two pad electrodes 11. The pad electrodes 11 are formed on the circuit board 10 using conventional PCB etching processes and are made of conductive metal, such as copper, copper foil, or copper alloy. The number of pad electrodes 11 is at least two, and they are spaced apart to form a conductive path with the temperature-sensing alloy 23. In this embodiment, the pad electrodes 11 can be disposed on the surface of the circuit board 10, such as... Figure 4As shown, the pad electrode 11 can also be embedded into the circuit board 10, such as... Figure 5 As shown, the specific design should be tailored to actual needs. Preferably, the surface of the pad electrode 11 can be treated with anti-oxidation treatment (such as gold plating or tin plating) to ensure reliable welding with the temperature-sensing alloy 23.

[0028] The temperature-sensitive alloy 23 is welded to the two pad electrodes 11 to form a conductive circuit. That is, the temperature-sensitive alloy 23 is directly electrically connected to the two pad electrodes 11 on the circuit board 10 to protect the protected component 3 on the circuit board 10. The temperature-sensitive alloy 23 is made of a low-melting-point alloy material to ensure that it rapidly heats up and melts due to its own thermal effect under a preset overload current, thereby breaking the conductive circuit and protecting the circuit. The shape of the temperature-sensitive alloy 23 is adapted to the spacing of the pad electrodes 11, and it is directly fixed between the two pad electrodes 11 through a welding process (such as laser welding, resistance welding, or hot welding) to form an electrical conductive circuit. The welding area must be free of cold solder joints to ensure stable conductivity at room temperature. As an example, the material of the temperature-sensitive alloy 23 includes, but is not limited to, metals such as indium, bismuth, antimony, and tin, and their alloys.

[0029] Please see Figure 3 The circuit board structure also includes a flux 22, which covers at least a portion of the surface of the temperature-sensitive alloy 23. The flux 22 is an organic resin composition with fluxing properties, applied to the surface of the temperature-sensitive alloy 23 through processes such as dispensing, spraying, filling, and coating. Its function is to promote rapid fracture of the alloy when it reaches its melting point, preventing arcing. The specific materials and structure of the flux 22 can utilize existing products capable of achieving the fluxing effect and are not limited here.

[0030] Please see Figure 4 The outer casing 21 is connected to the circuit board 10, and the temperature-sensing alloy 23 is sealed within the cavity formed by the outer casing 21 and the circuit board 10 to achieve sealed protection for the temperature-sensing alloy 23. The material of the outer casing 21 includes, but is not limited to, insulating materials such as plastic or ceramic. The structural shape of the outer casing 21 can be reasonably designed according to actual needs, and this embodiment is not limited thereto.

[0031] Preferably, the outer shell 21 is a ceramic shell, a plastic shell, or a pre-molded film shell. When the outer shell 21 is a ceramic shell, its material can be alumina ceramic; when the outer shell 21 is a plastic shell, its material can be a thermosetting resin, such as epoxy resin, UV resin, etc., formed by injection molding; when the outer shell 21 is a pre-molded film shell, the material of the outer shell 21 is PET, PEN, PA, PC, PVDF, PTFE, PI, PE, PP, PVC, or PS. Preferably, the thickness of the outer shell 21 is 0.02mm~0.2mm. Specific selection can be made according to actual needs, and this embodiment does not limit this. Compared with ceramic shells and injection-molded plastic shells, this embodiment preferably uses a thinner pre-molded film shell, which significantly reduces the height of the outer shell 21 and reduces the space occupied while ensuring the sealing effect, achieving extreme miniaturization of the temperature fuse composed of the temperature-sensing alloy 23, the outer shell 21, and the flux 22. This type of thermal fuse is better suited for high-density circuit board scenarios and can be flexibly embedded into more sophisticated electronic systems, avoiding the encroachment of traditional large thermal fuses on the board layout area.

[0032] Preferably, when the circuit board 10 is a flexible FPC board, the outer shell 21 is a thin-film preformed shell 21, and the temperature-sensitive alloy 23 is made of a soft alloy material. The soft alloy material has ductility matched to the FPC board, allowing it to bend without breaking, ensuring conductivity stability in a flexible environment. The joint between the thin-film preformed shell 21 and the FPC board is sealed with flexible adhesive resin to ensure that the shell 21 does not detach when the FPC board is bent, while maintaining an internal seal.

[0033] In an alternative embodiment, the outer shell 21 is a liquid resin encapsulation structure, wherein the liquid resin includes UV-curable resin or thermosetting resin, and the molding process of the liquid resin includes injection, spraying, impregnation, brushing, or roller coating. Specifically, after the temperature-sensitive alloy 23 and the fluxing agent 22 are assembled, the liquid resin is uniformly covered on the target area by a spraying process, and then cured by UV irradiation to form a sealed outer shell 21. This structure eliminates the need for a prefabricated shell, further reducing the overall size.

[0034] Traditionally, the casing and circuit board are connected by soldering. However, this soldering process is unreliable, the soldering effect is unsatisfactory, and the flux can easily seep out from the solder joint at high temperatures, affecting product performance. Therefore, to solve the above problems, please refer to [link to relevant documentation]. Figure 4In this embodiment, the outer casing 21 is preferably connected to the surface of the circuit board 10 via an adhesive resin layer 25. Traditional thermal fuses, as independent devices, require soldering, wave soldering, or other processes to be mounted onto the circuit board. Since thermal fuses are temperature-sensitive devices, the high-temperature environment of these soldering processes can easily cause premature damage or performance degradation of the temperature sensor, posing a risk of installation failure. This invention uses a thermosetting epoxy resin or acrylic adhesive for the adhesive resin layer 25, which is applied to the contact area between the outer casing 21 and the circuit board 10. After curing, it forms a sealed cavity, completely sealing the temperature-sensing alloy 23 and the flux 22, avoiding the risk of high-temperature damage during installation, thereby effectively improving product performance and preventing the influence of the external environment (such as moisture and dust) on internal components.

[0035] This embodiment achieves miniaturization and integration of the thermal fuse through the above-described circuit board structure design, while ensuring the response speed and reliability of over-temperature protection.

[0036] To further optimize conduction reliability and fuse accuracy, please refer to [link / reference]. Figure 6 , Figure 7 The temperature-sensitive alloy 23 adopts a differentiated structural design of "pre-welded molten layer 24 at the welding position and close contact with circuit board 10 at the non-welding position", which can prevent excessive consumption and prevent molten alloy accumulation.

[0037] Specifically, before the temperature-sensitive alloy 23 is soldered onto the circuit board, the thickness of the temperature-sensitive alloy 23 at the soldering position with the pad electrode 11 is greater than the thickness of the temperature-sensitive alloy 23 at the non-soldering position, forming a roughly gate-shaped or H-shaped structure. In this embodiment, by setting a larger thickness for the temperature-sensitive alloy 23 at the soldering position in contact with the pad electrode 11, the mechanical strength of the solder joint can be enhanced, preventing detachment due to vibration or thermal stress. Conversely, setting a thinner temperature-sensitive alloy 23 at the non-soldering position, such as by reducing the thickness or increasing the narrow diameter, can effectively reduce the heat capacity, causing the alloy to melt preferentially from the thinnest point when overheated, thus improving the protection response speed.

[0038] During the welding process of the temperature-sensitive alloy 23 onto the pad electrode 11, localized over-melting due to high temperatures is inevitable. If the thickness of the welding position is the same as that of the non-welding position, excessive melting can easily lead to excessive consumption of the temperature-sensitive alloy 23 in the welding area, and may even damage the stability of the temperature-sensitive alloy 23 structure, causing the connection between the alloy and the pad to be too thin or broken. Therefore, this embodiment designs the welding position to be thicker, reserving sufficient material for welding melting. Even if some alloy melts away during the welding process, the remaining thickness can still ensure a reliable connection between the temperature-sensitive alloy 23 and the pad electrode 11, avoiding structural collapse or connection failure due to over-melting, and ensuring the stability of the conductive circuit. Preferably, the temperature-sensitive alloy 23 includes a pre-welded molten layer 24, which is disposed at the welding position between the temperature-sensitive alloy 23 and the pad electrode 11. The pre-welded molten layer 24 and the temperature-sensitive alloy 23 can be made of the same material. That is, this embodiment utilizes the design of the pre-welded molten layer 24, which is integrally formed with the temperature-sensitive alloy 23, to ensure the thickness difference of the overall alloy in the welding area and the non-welding area of ​​the pad electrode 11. For example Figure 7 As shown, a pre-welded molten layer 24 is provided at the end where the temperature-sensitive alloy 23 is welded to the pad electrode 11, making the overall temperature-sensitive alloy 23 arch-shaped. When the temperature-sensitive alloy 23 is welded to the pad electrode 11, part of its pre-welded molten layer 24 will be melted.

[0039] Furthermore, the non-welded areas are critical for the melting of the temperature-sensitive alloy 23. If the welded area over-melts, excess molten material may flow to the non-welded areas, increasing their actual thickness. This increases the heat capacity of the non-welded area, delays the melting response time, and may even cause the melting temperature to rise, affecting the protection accuracy of the thermal fuse. In the differentiated thickness design, the thickness of the welded area absorbs excess melting during the welding process, reducing the diffusion of molten material to the non-welded areas. This ensures that the thickness of the non-welded areas meets design requirements, thereby ensuring timely and reliable melting at the set temperature and maintaining the normal protective function of the thermal fuse.

[0040] Furthermore, such as Figure 5 , Figure 6 As shown, after the temperature-sensing alloy 23 is soldered and installed to the pad electrode 11, at least a portion of the surface of the temperature-sensing alloy 23 near the circuit board 10 is in contact with the circuit board 10. Specifically, the surface of the temperature-sensing alloy 23 near the circuit board 10 is designed as a planar structure, wherein the two opposite ends of the temperature-sensing alloy 23 are in contact with the pad electrode 11, and the middle area is in direct contact with the surface of the circuit board 10. The surface of the circuit board 10 corresponding to the middle area of ​​the temperature-sensing alloy 23 is a flat insulating layer without any metal plating or protruding structure, ensuring that there is direct physical contact (non-soldering connection) between the temperature-sensing alloy 23 and the circuit board 10.

[0041] Through the above design, when the temperature-sensitive alloy 23 melts due to overheating, the molten alloy material shrinks due to the non-wetting properties of the insulating substrate of the circuit board 10, remaining only on the two side pad electrodes 11, without alloy accumulation or bridging in the middle area. Compared to the traditional design where there is a gap between the temperature-sensitive alloy and the circuit board (which may cause the molten alloy to form thin wire connections in the gap due to surface tension), this structure ensures that the gap between the two pad electrodes 11 is completely broken after separation, effectively reducing the risk of secondary conduction. In addition, the direct contact between the temperature-sensitive alloy 23 and the circuit board 10 can disperse the stress in the soldering area. That is, when the circuit board 10 is subjected to vibration or impact, the middle contact area can help fix the temperature-sensitive alloy 23, reducing the stress on the connection between the pad electrodes 11 and the alloy, and reducing the risk of solder joint detachment.

[0042] In an alternative implementation, this embodiment can achieve direct contact between the temperature-sensitive alloy 23 and the circuit board 10 by lowering the height of the pad electrode 11.

[0043] For specific implementation details, please refer to the following: Figure 5 The pad electrode 11 is embedded in the circuit board 10, and the surface of the pad electrode 11 near the temperature-sensitive alloy 23 is flush with the surface of the circuit board 10 near the temperature-sensitive alloy 23. During soldering, the pre-soldering molten layers 24 at both ends of the temperature-sensitive alloy 23 overlap the upper surface of the pad electrode 11. At this time, because the thickness of the two pre-soldering molten layers 24 of the temperature-sensitive alloy 23 is greater than the thickness of the non-soldering area, a gap is formed between the temperature-sensitive alloy 23 and the circuit board 10. After the soldering molten layers 24 are heated and melted, the temperature-sensitive alloy 23 is subjected to pressure, and the soldering molten layers 24 gradually fill the gap. After cooling and solidification, the soldering is completed, and the lower surface of the temperature-sensitive alloy 23 adheres to the circuit board 10 after being squeezed. That is, the pad electrode 11 is embedded in the circuit board 10, and the surface of the pad electrode 11 near the temperature-sensitive alloy 23 is on the same plane as the surface of the circuit board 10, without any protrusions or depressions. By designing the pad electrode 11 flush with the surface of the circuit board 10, not only can direct contact between the temperature sensing alloy 23 and the circuit board 10 be achieved, but the breakage of the temperature sensing alloy 23 caused by the pad protrusion is also avoided from the root.

[0044] Specifically, traditional raised pads are prone to accumulating temperature-sensitive alloy on their sides during welding or melting processes (especially in miniaturized structures where the distance between two pads is only 0.3mm~0.5mm), easily forming "alloy bridges" and leading to incomplete separation. This embodiment utilizes a flush-surface design, ensuring that the pad electrodes 11 have no exposed sides (or are covered by the substrate of the circuit board 10). When the temperature-sensitive alloy 23 melts, it only contracts and accumulates on the surface of the pads, while the area of ​​the circuit board 10 between the two pad electrodes 11 remains unwetted by the circuit board 10 substrate. After separation, the temperature-sensitive alloy 23 quickly contracts towards the two pad electrodes 11, further eliminating the risk of secondary conduction. Especially for flexible FPC boards, the flush-surface designed pad electrodes 11, compared to traditional raised pads which are prone to peeling from the substrate during FPC bending, effectively alleviate stress concentration caused by bending, thus improving the lifespan of flexible products.

[0045] In another alternative implementation, when a pre-welded molten layer 24 is provided at the welding position between the temperature-sensitive alloy 23 and the pad electrode 11, this embodiment can also achieve direct contact between the temperature-sensitive alloy 23 and the circuit board 10 by lowering the height of the pad electrode 11 and setting a limiting groove 11a.

[0046] For specific implementation details, please refer to [link / reference]. Figure 6The pad electrode 11 is embedded in the circuit board 10. A pre-soldering fusion layer 24 is provided at the welding position between the temperature-sensitive alloy 23 and the pad electrode 11. The pre-soldering fusion layer 24 increases the thickness of the temperature-sensitive alloy 23 so that the thickness at the welding position is greater than the thickness at the non-welding position. The pad electrode 11 is provided with a limiting groove 11a for placing the pre-soldering fusion layer 24. The pre-soldering fusion layer 24 can be placed at both ends of the temperature-sensitive alloy 23. The pre-soldering fusion layer 24 and the temperature-sensitive alloy 23 can be integrally made or separately made. Alternatively, the pre-soldering fusion layer 24 can be placed on the upper surface of the limiting groove 11a. The depth of the limiting groove 11a is less than or equal to the thickness of the pre-soldering fusion layer 24. In this case, the depth of the limiting groove 11a is equal to the thickness of the pre-soldering fusion layer 24. When the depth of the limiting groove 11a is equal to the thickness of the pre-soldering molten layer 24, after the pre-soldering molten layer 24 is placed into the limiting groove 11a, the lower surface of the temperature-sensitive alloy 23 adheres to the circuit board 10; when the depth of the limiting groove 11a is less than the thickness of the pre-soldering molten layer 24, after the pre-soldering molten layer 24 is placed into the limiting groove 11a, the temperature-sensitive alloy 23 is pressed down when the pre-soldering molten layer 24 melts, so that the lower surface of the temperature-sensitive alloy 23 adheres to the circuit board 10. The design of the limiting groove 11a allows the molten solder of the pre-welded molten layer 24 to fill the limiting groove 11a and form a metallurgical bond with the pad electrode 11. It can not only limit the flow range of the pre-welded molten layer 24, but also, in conjunction with the height difference design of the pad electrode 11, enable the temperature-sensitive alloy 23 to directly contact the circuit board 10 after welding; it can also constrain the distribution of molten solder and prevent solder from overflowing to the non-welded position of the temperature-sensitive alloy 23. After welding is completed, the molten solder of the pre-welded molten layer 24 is confined in the limiting groove 11a until it cools and solidifies to complete the welding.

[0047] Furthermore, to achieve accurate positioning between the housing 21 and the circuit board 10, this embodiment uses a concave-convex structure between the circuit board 10 and the housing 21 to achieve snap-fit ​​positioning. This not only improves assembly efficiency but also enhances the stability of the mechanical interlocking between the housing 21 and the circuit board 10, reducing the risk of the housing 21 falling off. Simultaneously, its precise positioning avoids localized sealing gaps caused by housing 21 misalignment, improving sealing reliability.

[0048] In a specific implementation, the circuit board 10 is provided with a recess 12 or a boss 13 for positioning the housing 21, and / or the housing 21 is provided with a protrusion 21a and a recess 21b for positioning the circuit board 10. The specific structure can be as follows: Figure 8 As shown, a boss 13 is pre-formed on the area of ​​the circuit board 10 that is joined to the housing 21, and a recess 21b matching the boss 13 is formed on the bottom of the housing 21 so that the two fit together and position on the circuit board 10; or, as Figure 9As shown, a recess 12 can be pre-formed in the area where the circuit board 10 and the housing 21 are joined, and a protrusion 21a matching the recess 12 is formed on the bottom of the housing 21 so that the two fit together and position on the circuit board 10; or, as shown Figure 10 As shown, a recess 12 can be pre-formed in the area where the circuit board 10 and the housing 21 are joined, and the bottom of the housing 21 is embedded in the recess 12; or, as shown Figure 11 As shown, bosses 13 are pre-formed on the circuit board 10 at the locations of the two outer sidewalls or two inner sidewalls of the housing 21, and the two outer sidewalls or two inner sidewalls of the housing 21 are positioned between the bosses 13. An adhesive resin layer can be used to connect the circuit board 10 and the housing 21 at the mating point.

[0049] It should be noted that the specific structure and quantity of the recess 12, boss 13, protrusion 21a, and recess 21b can be reasonably set according to actual needs, and this embodiment does not limit them here.

[0050] In other embodiments, the temperature-sensitive alloy 23 has a smaller dimension along its thickness direction than its dimension along its width direction. That is, the temperature-sensitive alloy 23 has a flat or cylindrical structure. Compared with the traditional wire-like structure, it directly reduces the space occupied perpendicular to the surface of the circuit board 10. Combined with the flush solder pad electrode 11 and the thin housing 21, the overall height of the thermal fuse can be greatly reduced, meeting the integration requirements of ultra-thin electronic devices. Furthermore, the larger dimension in the width direction increases the contact area between the temperature-sensitive alloy 23 and the solder pad electrode 11, which can increase structural stability and soldering stability.

[0051] Taking the circuit board structure with the integrated thermal fuse mentioned above as an example, the fabrication process of this circuit board structure can be as follows: a) Provide a circuit board 10 with pre-installed welding electrodes; b) Provide a temperature-sensitive alloy 23, and weld the temperature-sensitive alloy 23 onto the welding electrode on the circuit board 10 by laser welding, resistance welding or hot welding to form a conductive circuit. c) Apply, fill, or spray a layer of fluxing agent 22 onto the surface of the temperature-sensitive alloy 23; d) After the flux 22 has cooled and set, a UV-cured resin is injected onto the flux 22, and the UV-cured resin is cured by UV light to obtain the outer shell 21; or, an outer shell 21 is provided and the outer shell 21 is bonded to the circuit board 10 by an adhesive resin layer 25; so that the temperature-sensitive alloy 23 and the flux 22 are sealed in the cavity formed by the outer shell 21 and the circuit board 10.

[0052] It should be noted that, based on the above concept, and depending on the actual needs of the temperature fuse, those skilled in the art may also add other internal components to the temperature fuse, all of which fall within the protection scope of this utility model.

[0053] Example 2 This embodiment also provides a protection device, which includes a circuit board structure using an integrated thermal fuse as described in Embodiment 1 above. The specific design of the circuit board structure can be referred to the description in Embodiment 1 above, and will not be repeated here.

[0054] Among them, such as Figure 2 As shown, the circuit board structure includes a protected element 3, and at least one pin of the protected element 3 is the pad electrode 11. That is, the temperature-sensing alloy 23 and the protected element 3 share the same pad electrode 11 to achieve series connection. This design not only simplifies the pin processing and soldering process of the thermal fuse and reduces the impact of high-temperature soldering on the temperature-sensing alloy 23, but also increases heat transfer efficiency, improves temperature response speed, and achieves rapid disconnection.

[0055] In summary, the integrated temperature fuse circuit structure and protection device provided by this utility model achieves multi-dimensional technical effects through the innovative design of integrating the temperature fuse onto the circuit board, combined with the optimization of key structures such as the temperature-sensing alloy, solder pad electrodes, and housing, as detailed below: 1. Achieve high integration and miniaturization: By directly connecting the temperature-sensing alloy to the pad electrodes on the circuit board, the independent pins and package structure of traditional thermal fuses are eliminated. At the same time, the flat temperature-sensing alloy, flush-embedded pad electrodes, and thin-film shell can significantly reduce the overall size of the device, directly adapting to the space requirements of high-density, miniaturized circuit boards and improving the flexibility of circuit layout.

[0056] 2. Improved temperature response speed and protection accuracy: By utilizing the direct contact between the temperature-sensing alloy and the circuit board pads, the heat conduction path is shortened, enabling the temperature-sensing element to detect the actual temperature changes of the circuit board more quickly; at the same time, the flux directly covers the surface of the temperature-sensing alloy, which can quickly promote alloy melting when overheating, further improving the response speed and action accuracy of overheat protection.

[0057] 3. Enhanced packaging reliability and environmental adaptability: The outer shell is directly connected to the circuit board through the bonding resin layer, forming a closed cavity that seals the temperature-sensitive alloy and flux. This effectively prevents flux loss or interference from the external environment (such as moisture and dust), and avoids the risk of poor contact caused by pin soldering in traditional packaging, thus improving the long-term operational reliability of the device.

[0058] 4. Simplified installation process and reduced production risk: Eliminating the need for pin processing and secondary soldering of traditional independently packaged devices, this embodiment utilizes low-temperature processes such as laser soldering to weld the temperature-sensitive alloy after the circuit board reflow soldering process. This effectively avoids damage to the temperature-sensitive alloy caused by traditional high-temperature processes such as brazing and wave soldering. Furthermore, the contact area between the temperature-sensitive alloy and the solder pads is designed with a greater thickness (to compensate for soldering melt loss), reducing structural damage or cold solder joints caused by over-melting and improving soldering yield.

[0059] 5. Improve assembly accuracy and structural reliability; the concave-convex positioning structure between the circuit board and the shell enables quick positioning and snapping. At the same time, the mechanical interlocking of the convex structure and the bonding of the adhesive resin layer form a double fixation, which effectively improves the shell's resistance to vibration and impact, and avoids the risk of local sealing gaps caused by shell displacement.

[0060] 6. Optimized breaking performance to ensure reliable protection: The flush-surfaced electrode pads prevent alloy buildup on the sides. The bottom of the temperature-sensing alloy contacts the insulating substrate of the circuit board (the substrate does not wet the alloy). When melting, the alloy only shrinks and gathers on the side pads, leaving no residual bridging in the middle, ensuring a more thorough break and effectively eliminating the risk of secondary conduction. Furthermore, the temperature-sensing alloy uses a differentiated thickness design (thicker at contact points, thinner at non-contact points). The low heat capacity in the non-contact area allows for timely melting at the set temperature, avoiding temperature deviation due to over-melting.

[0061] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of this utility model can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.

[0062] Although this document frequently uses terms such as circuit board, solder pad electrode, housing, temperature-sensitive alloy, pre-soldering fusion layer, flux, and adhesive resin layer, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention. The terms "first," "second," etc. (if present), in the description, claims, and accompanying drawings of the embodiments of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. A circuit board structure integrated with a temperature fuse, characterized by, include: A circuit board having at least two solder pad electrodes. A temperature-sensitive alloy is welded onto two electrode pads to form a conductive circuit. The housing is connected to the circuit board, and the temperature-sensitive alloy is sealed within the cavity formed by the housing and the circuit board.

2. The integrated temperature fuse circuit board structure according to claim 1, characterized in that: The circuit board is provided with recesses or protrusions for positioning the housing, and / or the housing is provided with protrusions and recesses for positioning in conjunction with the circuit board.

3. The integrated temperature fuse circuit board structure of claim 1, wherein: The outer shell is a ceramic shell, a plastic shell, or a pre-formed film shell; when the outer shell is a pre-formed film shell, the material of the outer shell is PET, PEN, PA, PC, PVDF, PTFE, PI, PE, PP, PVC, or PS.

4. The integrated temperature fuse circuit board structure of claim 1, wherein: The circuit board is a rigid PCB board or a flexible FPC board; the circuit board is a single-layer board or a multi-layer board.

5. The integrated temperature fuse circuit board structure of claim 1, wherein: The outer shell is a liquid resin coating structure, the liquid resin including UV-curable resin or thermosetting resin, and the molding process of the liquid resin includes injection, spraying, brushing, dipping or roller coating.

6. The integrated temperature fuse circuit board structure of claim 1, wherein: Before the temperature-sensitive alloy is welded to the pad electrode, the thickness of the temperature-sensitive alloy at the welding position is greater than the thickness of the temperature-sensitive alloy at the non-welding position.

7. The integrated temperature fuse circuit board structure of claim 1, wherein: After the temperature-sensitive alloy is soldered to the pad electrode, at least a portion of the surface of the temperature-sensitive alloy is in contact with the circuit board on the side closest to the circuit board.

8. The circuit board structure of claim 7, wherein: The pad electrode is embedded in the circuit board, and the surface of the pad electrode near the temperature-sensitive alloy is flush with the surface of the circuit board near the temperature-sensitive alloy. After being squeezed, the lower surface of the temperature-sensitive alloy adheres to the circuit board.

9. The circuit board structure of claim 7, wherein: The pad electrode is embedded in the circuit board, and a pre-soldering molten layer is provided at the welding position between the temperature-sensitive alloy and the pad electrode. The pre-soldering molten layer increases the thickness of the temperature-sensitive alloy. The pad electrode is provided with a limiting groove for placing the pre-soldering molten layer, and the lower surface of the temperature-sensitive alloy is attached to the circuit board.

10. A protection device characterized by: The circuit board structure includes an integrated thermal fuse as described in any one of claims 1 to 9; the circuit board is provided with a protected element, and at least one pin of the protected element is the pad electrode.

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